The invention relates to a method for processing organic material and in particular to a method where carbon dioxide or a carbon dioxide-containing gas mixture and ammonia or ammonia-containing material are combined to form buffer compounds, and to an apparatus for implementing the method.
U.S. Pat. No. 4,824,571 discloses a method and an apparatus for degradation of various organic products and wastes in an anaerobic medium. The method generates degraded products and biogas. In the method, the mass to be degraded is introduced into a fermentation vat and the produced biogas is recovered. After this, the biogas is fed back into the vat from the bottom so as to provide a fluidization effect.
U.S. Pat. No. 4,302,236 discloses the use of a composting system for scrubbing gas effluvia. The method comprises removing inorganic acid-forming constituents from a gas stream high in sulphur, in particular. Inorganic groups form inorganic acids in the presence of oxygen or water. The gas stream to be cleaned is guided through active composting biodegradable organic waste, which is held under thermophilic bacteria-phase digestion conditions.
WO publication 93/06 064 discloses a method for neutralizing and recovering gases formed in connection with wet composting. The object of the invention described in the publication is to render harmful, toxic and/or polluting manure gases harmless. According to the publication, part of the gases is recycled to the composed mass so as to improve its nutrient value.
DE publication 3,134,980 discloses a method for mixing biomass in oxygen-free environment in a biogas reactor by means of biogas produced by bacterial strains and stored in biogas storage. In the method, the biogas is mixed with periodic biogas blows. The necessary biogas pressure is provided by means of the bacterial strains in the biogas reactor. The reactor is externally closed and it communicates with the biogas pressure vessel. Pressure is released in the biogas pressure vessel and next it is blown into the biomass, from which the biogas is further conducted into a biogas container.
EP application 486,466 discloses a method for controlled and continuous aerobic biological decomposition of organic wastes. Decomposing material, which is optionally inoculated with a mixture of bacteria and microbes, is fed into the material in the microbiological waste and the degraded material is removed, whereby an oxygen-containing gas is passed in for the degradation. The object of the method described in the publication is to control the degradation of nitrogen-containing products. In the method, CO2 gas is added to the oxygen-containing gas, depending on the NH3 content and the pH of the degradation product, whereby the gas is mixed with a fraction containing no or very little nitrogen. The method described in the publication is an aerobic method.
Organic material is received from various sources from products of plant and animal origins. One problem with organic material degradation plants is that availability of material to be processed is season-dependent and the plant must be able to process even large amounts of organic solids within a short period because they do not allow long storage. Preservation of organic material poses several problems; for instance, preservation produces NH3, which is a toxic compound and prevents microbes from functioning. Currently the bioconversion reactors allow introduction of only low solid contents because NH3 prevents the microbial function in the reactors. Preservation of seasonally produced organic material also causes problems because it cannot be preserved in acidic or basic conditions if conventional bioconversion processes are employed since they are sensitive to variations in the pH. Conventional bioconversion processes are also extremely sensitive to changes in temperature.
A biogas combustion plant is often arranged in connection with a bioconversion plant for combustion of biogas produced in the bioconversion process. The exhaust gas produced in the biogas combustion has a high carbon dioxide content. However, carbon dioxide is a harmful compound to the environment and there is a general objective to get rid of it.